(1) Field of the Invention
The invention pertains to the formation of amine alanes, AlH.sub.3.NR.sub.3. These materials are useful as chemical intermediates. For example, they can be reacted with a silicon halide such as SiCl.sub.4 or SiF.sub.4 to produce silane.
(2) Related Art
Reference is made to U.S. Pat. No. 4,474,743. It pertains to production of silane and aluminum fluoride from silicon tetrafluoride and amine alanes. Reference is also made to U.S. Pat. No. 4,006,095. It teaches, inter alia, that SiCl.sub.4 reacts with a toluene solution of AlH.sub.3 containing dimethyl ether or a stabilizing amine.
U.S. Pat. No. 4,474,743, cited above, contains a citation to U.S. Pat. No. 4,006,095. It also sets forth other prior art relating to amine alane production. For example, it sets forth the following general methods for preparing amine alanes: ##STR1##
U.S. Pat. No. 4,474,743 also states that:
"Alane, that is aluminum trihydride or AlH.sub.3, has in the past been produced from the reaction of LiAlH.sub.4 and AlCl.sub.3 in ethers. Also known is the production of an alane dimethyl ether solution from the reaction of LiH and AlCl.sub.3 in dimethyl ether, catalyzed by NaAlH.sub.4.
Amines are used to produce amine alanes for subsequent syntheses. For example, LiAlH.sub.4 can be reacted with a trialkyl amine.HCl complex to precipitate LiCl and form AlH.sub.3.NR.sub.3 where R is alkyl."
Of particular interest is the reaction given by Equation (3). As illustrated by the equation, it is known that amine hydrochlorides can react with sodium aluminum hydride to prepare amine alanes, sodium chloride, and hydrogen. This reaction is similar to that using LiAlH.sub.4 reported in the paper by Ruff et al, J. Am. Chem. Soc. 82 pp 2141-2144 (1960).
The process of the instant invention is distinct from the process of Equation (3) since the instant process does not use pre-formed amine hydrochlorides. In other words, the process of this invention comprises bringing together in uncombined form, an amine and a hydrogen halide (such as HCl) for reaction with a complex metal aluminum hydride. Thus for example, the process of this invention can be conducted by forming a mixture of alkali metal aluminum hydride and tertiary amine, and then adding the hydrogen halide to the aforesaid mixture. Alternatively, the process of this invention can be conducted by adding an alkali metal aluminum hydride such as NaAlH.sub.4 to a reaction zone, and then simultaneously (or substantially simultaneously) adding the amine and hydrogen halide of choice to the complex metal hydride, thereby causing the added starting materials to react and form the products of this invention.
The process of this invention is not obvious from the prior art. In fact, it is contrary to what the art suggests. Thus, Ruff et al, loc cit suggests to a skilled practitioner that it is necessary to use a pre-formed amine hydrochloride. Ashby "The Chemistry of Complex Aluminohydrides": Adv. Inorg. Chem. Radiochem. 8 (1966) pp. 295 and 310, teaches that protic and halogen acids would react violently with LiAlH.sub.4 to liberate hydrogen. On the other hand, Brown, et al J. Am. Chem. Soc. 88 1464-72 (1966) reports that 100% sulfuric acid can be added to a THF solution of LiAlH.sub.4 to evolve hydrogen and produce a solution of aluminum hydride. However, in neither case was any evidence presented as to what would occur when the acid is added to a suspension of the complex aluminum hydride in an inert solvent such as toluene. From a combination of the Ruff et al, and Ashby references, a skilled practitioner might conclude that the process of this invention would not work, since the complex metal hydride and the hydrogen halide could interact in a deleterious way, making them both unavailable for reacting according to the process of this invention.
The process of this invention is conducted by contacting the reactants under reaction conditions. Furthermore, as indicated above, it does not require pre-formed amine hydrochlorides used in the art. Thus, in one aspect, the invention comprises a process for reacting a complex metal hydride, an amine, and a hydrogen halide; said process being conducted in the substantial absence of added pre-formed amine hydrohalide.
The process of this invention does not require an ether reaction medium utilized by Ruff et al. Although, the process of this invention can be conducted in the presence of an ether, it is preferred that it be conducted in the substantial absence of ethers.